Background: for many centuries, herbs and herbal extracts have been used as a treatment for diseases. Today, many medicines are derived from herbal sources. Herbs for treatment purposes are the source of many modern medicine treatments. Materials and Methods: In this experimental study, the hydroalcoholic extract of Amaranthus Retroflexus L. seeds was prepared, then the required concentrations for the experimental stages were prepared and MTT test was performed on the CT26 and MRC5 cells. Simultaneously, tumor induction was performed in mice. The clone tissue was sampled, RNA was extracted, and finally, the cDNA was implemented. The results of gene expression changes were evaluated by RealTime technique with the t-test and ANOVA. Results: Amaranthus Retroflexus L. seed extract reduced the survival and proliferation of cancer cells. The decrease in cell survival depends on concentration, and this decrease is significant (p <0.05). Moreover, Cox2 and Her2 gene expression increased significantly on day 28 and then significantly decreased after the treatment with the extract (p <0.05). Conclusion: Treatment with Amaranthus Retroflexus L. seed extract decreased gene expression and cell proliferation in cell lines. Therefore, the extract of this plant can be used to improve cell proliferation and cancer cells.